As I start to think about transitioning to HPR, I realize that I have little to no knowledge of what kind of epoxy to use to make larger rockets such as Madcow's Super DX3 or something on that scale.
Is there a good source around for learning the ways of epoxy? Or is it all a lot simpler than my beginner's mind is thinking?
Thanks!
I wish !!!! I have been working with Epoxy and Epoxy based resins for over 20 years and much of that time I have been doing in professionally. I have had my own shop doing composite work and I worked in an Aerospace R&D shop. When I started out there was very little in any information that was easily accessible. I learned a lot through filling garbage cans, maybe we can save you that step.
There are a few "basic" rules to understand with epoxy and epoxy based resins.
The faster they cure the hotter they get as they cure. They all exo-therm but I have used some that will burn if you get some on your gloved finger. Slower curing epoxies give off less heat and are normally less brittle when cured. This is important to those building HPR's because of the stresses the rockets endure during launch.
Thickening agents such as micro balloons, flour, or Cabosil accelerate curing which causes more heat. I mention heat again because it can be enough to deform a nose cone. If you are filling the tip of a nose cone put it in a bucket of ice.
Most good epoxies have a very long shelf life but they do not respond well to thermal cycling. Once mixed you have what ever working time your resin allows.
Post curing in a hot box or curing oven always helps. This is for after the initial cure is done.
Even a 30 minute epoxy is not up to full strength for at least 24hrs. I have used lay-up resin that was "cured" in my hot box for 24 hrs and was basically done but would not reach full hardness for another 7 days.
Latex clothes will not stop the chemicals that cause the allergic issues. I now have a bad allergy to epoxy because I did not know this 15 years ago. Now if epoxy gets on my hands I have to pour water that is close to boiling to stop the itching. Nitrile gloves are the key here.
The key to working with epoxies is prep. make sure EVERYTHING is laid out and ready. I suggest you even move through the motions of the process just to make sure you are not putting something where it can get bumped, knocked over or contaminated.
If you are doing a decent sized mix, pour it out on a paper or foam plate. This will give you more working time because it will slow the cure. Leaving it in the cup accelerates the cure. I had a buddy skip this step and melt a plastic cup because the epoxy got so hot sitting in the cup while he worked on something.
For most of us the 30 minute Epoxy from Hobby Lobby works great. If you want to get into fiberglassing tubes and fins or even rolling your own tubes get in touch with me as there are some more tricks I can share. If you looking for a serious Epoxy and want to step things up take a look at Resin Research. Their resins as as good as any and better than most. They even have a hardener that is comparable to hobby epoxy for curing time but the mechanical values surpass anything we can find in a hobby shop.
Oh, the BIG TIP...Vinegar will clean up un-cured epoxy.